1. Field of Invention
The present invention relates to a method and an instrument for revision arthroplasty for the removal of thermoplastic polymer cement set in a bone cavity after the loosened or defective prosthesis component is removed from its anchoring in the cement. More specifically, but not exclusively, the present method applies to the removal of polymethylmethacrylate cement casted in a femur cavity.
2. Description of Prior Art
It is common practice, in revision arthroplasty, to utilize chisels and hammers as well as high speed turbine drills in order to remove set thermoplastic polymer cement which is embedded in a bone cavity to secure a prosthesis component therein. This cement is usually removed by chiselling at the cement from the neck of the bone cavity after the prosthesis component has been dislodged from the cement. It is possible to insert instruments through this cavity and chisel away at the wall of the cement. A problem with this method is that often whilst chiselling away, a piece of the bone will be cut away or break off by the impact of the chisel. A further method is to insert a drill bit through the neck of the bone cavity and again, the cutting edges of the drill will often penetrate or scrape off portions of the bone. The reason for this is that the surgeon is unaware of how close the bone wall is to the inner cement wall being worked on.
It is often necessary, particularly in order to remove this plastic cement from the bottom of the bone cavity, to make a window or gutter or hole in the bone side wall by the use of a drill and to chip at the cement through this window. Again, because these drills are high speed and have sharp cutting elements, often the bone is penetrated through, thus damaging and weakening the bone. Another disadvantage of the prior art methods is that it is often difficult to remove all of the cement from the bone cavity and often loose chips may remain within the cavity.
There are other disadvantages of these prior art methods. For example, the high speed turbine drills are extremely costly, and they generate a fine powder while drilling through the hardened cement and this powder dirties the area around the incision making it more difficult to work and disinfect. These prior art methods are also very time-consuming and the devices are bulky and difficult to handle.
A common revision arthroplasty relates to the hip joint femoral prosthesis where an estimated 20,000 revisions are effected annually and such revisions are on the increase.